FIG. 1 illustrates an example of a conventional wireless (mobile) communication system. The wireless (mobile) communication system 100 includes a plurality of Base Stations (BSs) 110a, 110b and 110c and a plurality of User Equipments (UEs) 120a to 120i. Each BS 110a, 110b or 110c provides services to its specific geographical area 102a, 102b or 102c, which may further be divided into a plurality of smaller areas 104a, 104b and 104c. In a downlink, a transmitting end includes the BS and a receiving end includes the UE. In an uplink, the transmitting end includes the UE and the receiving end includes the BS.
Recently, the demand for wireless communication services has risen abruptly due to the generalization of information communication services, the advent of various multimedia services and the appearance of high-quality services. To actively cope with the demand, a communication system's capacity should first be increased. In order to do so, methods for finding new available frequency bands and raising the efficiency of given resources in wireless communication environments are considered.
Much effort and attention has been made to research and develop multi-antenna technology. Here, diversity gain is obtained by additionally securing a spatial area for resource utilization with a plurality of antennas provided to a transceiver or raising transmission capacity by transmitting data in parallel via each antenna.
An example of a multi-antenna technology is a multiple input multiple output (MIMO) scheme. The MIMO scheme indicates an antenna system having multiple inputs and outputs, raises a quantity of information by transmitting different information via each transmitting antenna, and enhances reliability of transport information using coding schemes such as STC (space-time coding), STBC (space-time block coding), SFBC (space-frequency block coding) and the like.